Method for detecting straight-ahead driving based on information on the rotational speed of a wheel

ABSTRACT

The present invention relates to a method of detecting straight-ahead driving according to a first straight-ahead driving detection method based on information on the rotational speed of a wheel by way of memorizing a curve parameter in a learning phase, in particular in selected driving situations, and the curve parameter is formed from the wheel speed information of one or more axles, and the reciprocal value of the curve radius is calculated from the wheel speed information to determine the curve parameter. The invention also relates to a computer program product comprising an algorithm defined by the above method.

TECHNICAL FIELD

The present invention relates to a method for detecting straight-aheaddriving based on information on the rotational speed of a wheel and acomputer program product.

BACKGROUND OF THE INVENTION

In motor vehicles with brake systems equipped with ABS control, drivingdynamics control, or similar systems, it is conventional practice inelectronic control devices to implement most different methods fordetecting driving situations by way of a microprocessor. In practicallyall methods for detecting the driving situation, input signals of wheelspeed sensors for detecting the driving situation are evaluated eitheralone or jointly with further sensors (yaw rate, transverseacceleration, etc.) if these further sensors (so-called ESP sensorequipment) are provided in the vehicle.

DE-A 100 58 140 discloses, for example, that tire pressure losses can bedetected on the basis of wheel speed information alone. A basiccondition for a high-quality detection is the reliable detection ofdriving situations that are appropriate for determining data. Aparticularly appropriate driving situation for determining data is thestraight-ahead driving of the vehicle.

BRIEF SUMMARY OF THE INVENTION

Previously attempts have been made according to the state of the art todetermine the yaw rate or the transverse acceleration from the wheelspeed information as precisely as possible in order to detect straighttravel.

The invention at issue departs from this idea and instead takes intoaccount inverted curve radii calculated from the wheel speeds. It hassurprisingly shown that an examination of the inverted curve radii leadsto a higher rate of precision when this principle is used in a per seknown pressure loss detection method on the basis of wheel speed sensors(DDS: Deflation Detection System, see EP-A 0 983 154).

In view of the above, the invention relates to a method of detectingstraight-ahead driving according to a first straight-ahead drivingdetection method on the basis of wheel speed information by memorizing acurve parameter in a learning phase, in particular in selected drivingsituations, wherein the curve parameter is formed from the wheel speedinformation of one or more axles, and the reciprocal value of the curveradius is calculated from the wheel speed information to determine thecurve parameter.

The said reciprocal value is preferably derived from the ratio ofrotational speeds between front wheels and rear wheels. According toanother preferred embodiment of the invention, an inverted curve radiusis formed and, more particularly, memorized, separately for the frontaxle and the rear axle.

The reciprocal value is filtered especially mathematically according toa per se known algorithm. Said algorithm is preferably a recursivefiltering method which is advantageous in terms of a low consumption ofmemory locations, as described in DE 100 34 224 A1, for example.

Current appropriate curve values are memorized during thereciprocal-values learning phase so that the statistic quality of thelearnt value is normally constantly improved. Preferably, the learningphase is terminated when a scatter quantity that has to be suitablyselected falls below a threshold value. Appropriate curve values arepreferably those for which the inverted curve radius falls below apredetermined threshold value.

In the phase of comparison that follows the learning phase after thelearning phase is completed, the DDS system is preferably deactivatedonly when cornering is detected simultaneously on both axles (likewiseexamination of threshold values). For this reason, any pressure lossoccurring on an axle cannot deactivate the system.

It is preferred that the currently determined curve parameter isaveraged and/or filtered. The memorized curve parameter is alsofavorably averaged and/or filtered.

Advantageously, the curve parameters are memorized individually forseveral speed intervals, e.g. in a first speed interval of 15 km/h up to70 km/h, in a second speed interval of 70 km/h up to 100 km/h, in athird speed interval of 100 km/h up to 130 km/h, etc.

The curve parameter is favorably memorized in the driving situation‘straight-ahead driving’, and a second straight-ahead driving detectionmethod is used for detecting this driving condition.

A coarse detection of straight-ahead driving can be executed by way of aseparate method (second straight-ahead driving detection method).Favorably, already memorized values of the first straight-ahead drivingdetection method are ignored when a cornering maneuver is detected bymeans of the second straight-ahead driving detection method. This secondmethod detects in particular when the assumption ‘straight-aheaddriving’ was not sufficiently precise for learning the inverting curveradii. The learnt value is then omitted. Criteria foractivating/deactivating DDS can be derived from an estimated yaw rateand transverse acceleration.

The memorized curve parameter(s) is(are) preferably taken into accountto calculate real driving parameters such as curve radius, vehicle yawrate, and/or vehicle transverse acceleration.

Advantageously, the memorized curve parameter is taken into account forcalculating the driving parameter ‘actual curve radius’.

The first method for cornering detection is preferably integrated into amethod for detecting tire pressure loss on the basis of wheel speedinformation. The first method for cornering detection is especiallytaken into consideration for activating and/or deactivating saidpressure loss detection method.

The above-mentioned driving parameters such as yaw rate or transverseacceleration are favorably taken into consideration for activatingand/or deactivating the pressure loss detection.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinbelow, the method of detecting straight-ahead driving will beexplained by taking into account the method for pressure loss detectionin tires of motor vehicles as described in DE 100 58 140 A1. DE 100 58140 A1 discloses a method for straight-ahead driving detection on thebasis of yaw rate information. The straight-ahead driving detection orcornering detection represents an important output quantity for a tirepressure loss detection method based on wheel speed information. E.g.the rotational speed of an inside wheel in a turn differs from therotational speed of an outside wheel in a turn due to a corneringmaneuver. A prior art tire pressure loss detection method is unable torecognize whether the rotational speed variation is caused by pressureloss or by a cornering maneuver, with the result that undesirablespurious alarms may occur, or only very long observation times areallowed to be used for an alarm. It is therefore absolutely necessaryfor safe and quick pressure loss detection that cornering orstraight-ahead driving is safely detected. Prior-art tire pressure lossdetection methods use a yaw rate sensor for this purpose, which is e.g.provided in an ESP system. Because not all the vehicles are equippedwith an ESP system, the method of the invention describes astraight-ahead driving detection on the basis of the existing wheelspeed sensors. The method described in the following is especially usedin connection with a tire pressure loss detection method, and the tirepressure loss detection method is not performed until the straight-aheaddriving detection method has detected straight-ahead driving. Or,respectively, the tire pressure loss detection method is not performedwhen the cornering detection method has detected cornering.Straight-ahead driving detection or cornering detection must be regardedas equivalent in this case because it is insignificant whether the tirepressure loss detection method is performed only after detection ofstraight-ahead driving or is interrupted by the detection of a corneringmaneuver.

Exactly as the prior-art tire pressure loss detection method (DDS), themethod of the invention is started by way of actuating a reset button.It is necessary to this end that the driver has adjusted the prescribednominal pressure in all tires before the reset button is actuated. Aseven tires of the same type have discrepancies with respect to eachother, e.g. in terms of their rolling radii or their speed-responsiveexpansion, it is necessary to memorize these tire irregularities. Saidtire irregularities are memorized in a learning phase as so-calledoffset values in the form of learnt inverted curve radii per vehicleaxle in different speed intervals. The learnt inverted curve radius isessentially composed of a quotient, the numerator exhibiting thedifference between the wheel speeds of an axle, or values proportionalto the wheel speeds, while the denominator is composed of themultiplication of the vehicle's track width and the vehicle referencespeed. E.g. the vehicle speed calculated by an ABS is used herein as thevehicle reference speed. Further, the quotient can be extended byadditional scale factors to shift the learnt inverted curve radii intosuitable ranges of values (e.g. for integral calculus). An invertedcurve radius for each vehicle axle is learnt, and these learnt invertedcurve radii permit determining in addition values describing a yaw rateor a transverse acceleration. The learnt inverted curve radii and theadditional values (yaw rate, transverse acceleration) are stored in amemory (EEPROM). In addition, the learnt inverted curve radii can befiltered and stored according to generally known algorithms. The tirepressure loss detection method (DDS) remains deactivated during thereciprocal-values learning phase. The reciprocal-values learning phaseis terminated when a scatter quantity that must be selectedappropriately falls below a threshold value. Nevertheless, the invertedcurve radii are stored in a long-term storage and constantly comparedwith currently determined inverted curve radii in order to ensure thatactually it was the straight travel defined in the reciprocal-valueslearning phase that prevailed rather than a long cornering maneuver.

In a subsequent phase of comparison, currently established invertedcurve radii are determined for each axle from the wheel speeds, asdescribed in the reciprocal-values learning phase. These currentlydetermined inverted curve radii are compared with the learnt invertedcurve radii. If cornering is detected simultaneously on both axles, DDSis deactivated. If only one axle exhibits straight travel, DDS remainsactive.

Alternatively, it is also possible to use only the freely rolling axleas a reference for straight-ahead driving because a superposition of acornering maneuver with a driving torque on one or both driven wheels ofthe driven axle can induce a wrong interpretation with respect to aprevailing straight travel. In this respect, the inverted curve radiiare continuously monitored in the long-term storage as describedhereinabove. If it is detected in a comparison of the values for thelearnt inverted curve radii stored in the long-term storage that acurrently determined inverted curve radius rather describesstraight-ahead driving, a new start of the reciprocal-values learningphase is carried out. Likewise values for a determined yaw rate and adetermined transverse acceleration can be defined from the determinedinverted curve radii. This helps now as before achieving a qualitativelygood straight-ahead driving detection even in the case of pressure losson the freely rolling axle.

The method of the invention is favorably used for activating ordeactivating a tire pressure loss detection method (DDS) that determinespressure loss on the basis of the wheel speed information. Either theinverted curve radii or the yaw rates or transverse accelerationscalculated therefrom can be used as selection criteria in thisarrangement.

1-11. (canceled)
 12. Method for detecting straight-ahead drivingaccording to a first straight-ahead driving detection method on thebasis of wheel speed information by memorizing a curve parameter in alearning phase, wherein the curve parameter is formed from the wheelspeed information for at least one axle, and the reciprocal value of thecurve radius is calculated from the wheel speed information to determinethe curve parameter.
 13. Method as claimed in claim 12, wherein thecurrently determined curve parameter is averaged.
 14. Method as claimedin claim 12, wherein the currently determined curve parameter isfiltered.
 15. Method as claimed in claim 12, wherein the memorized curveparameter is averaged.
 16. Method as claimed in claim 12, wherein thememorized curve parameter is filtered.
 17. Method as claimed in claim12, wherein curve parameters for several speed intervals are memorizedindividually.
 18. Method as claimed in claim 12, wherein the curveparameter is memorized in the driving situation ‘straight-aheaddriving’, and a second straight-ahead driving detection method is usedfor detecting this driving condition.
 19. Method as claimed in claim 18,wherein already memorized values of the first straight-ahead drivingdetection method are ignored when a cornering maneuver is detected bymeans of the second straight-ahead driving detection method.
 20. Methodas claimed in claim 12, wherein the memorized curve parameter is takeninto account to calculate driving parameters.
 21. Method as claimed inclaim 12, wherein the memorized curve parameter is taken into accountfor calculating the driving parameter ‘actual curve radius’.
 22. Methodas claimed in claim 12, wherein the first method for cornering detectionis integrated into a method for detecting tire pressure loss on thebasis of wheel speed information, and the first method for corneringdetection is taken into consideration especially for activating saidpressure loss detection method.
 23. Method as claimed in claim 12,wherein the first method for cornering detection is integrated into amethod for detecting tire pressure loss on the basis of wheel speedinformation, and the first method for cornering detection is taken intoconsideration especially for deactivating said pressure loss detectionmethod.
 24. Method as claimed in claim 22, wherein the drivingparameters are taken into consideration for activating.
 25. Method asclaimed in claim 23, wherein the driving parameters are taken intoconsideration for deactivating.
 26. Computer program product defining analgorithm comprising a method as claimed in claim 12.